In our co-pending International patent application published under No. WO 2004008261 we describe a wireless communication system employing spread spectrum communication for controlling operation of networked communication devices such as battery powered light units for an emergency lighting system to assist evacuation of the aircraft in an emergency.
In our aforesaid application, the devices communicate wirelessly with a master controller and are arranged to cycle between an operable (awake) condition in which they can respond directly or indirectly to a signal transmitted by the master controller and an inoperable (sleep) condition in which they cannot respond to such a signal.
By arranging the devices to re-transmit any broadcast signal, not all the devices have to be within range of the master controller and synchronisation of the wake/sleep cycle of the devices is not required. As a result, battery power is conserved and the effective life of the battery can be usefully extended without significantly affecting the overall response of the system to a signal transmitted by the master controller.
In the application to networked devices for emergency lighting, each light unit preferably employs light emitting diodes (LEDs). Typically an array of LEDs is employed requiring a low power consumption whereby the level and duration of light output can be achieved to comply with regulatory requirements using a small battery.
The present invention seeks to develop and provide further improvements in and relating to onboard equipment employed in aircraft and the like especially wireless communication devices of the type described in our aforesaid International patent application.